The method described herein relates generally to generator inspection. More specifically, the method relates to inspecting a wye ring in a generator.
At least some known wind turbines include machines for converting variable speed mechanical input from blades of the wind turbine into electric power that is compliant with an electrical grid. For example, wind turbines may include a doubly fed induction generator (DFIG) for converting the variable speed mechanical input.
Some known DFIG generator rotors have a floating neutral point. This is frequently provided by a wye ring. The wye ring is typically made from a copper bar and is located at the non-drive end (NDE) of the generator. Due to operational stresses which fatigue the brazed connection between the wye ring and its rotor connection points (or connection lugs), cracks can develop which lead to discontinuity. When the first crack occurs, the generator continues to function satisfactorily since the current can still reach all three rotor connection points. However, if a second crack occurs in the wye ring, at least one part (e.g., one phase) of the rotor windings are now disconnected from the floating neutral. This results in severe arcing across one of the cracks, and leads to failure of the insulation around the wye ring. Eventually, cross-over arcing occurs between the wye ring and the phase lead, and significant damage can occur (e.g., fire). The wind turbine monitoring system detects this cross-over arcing condition and recognizes it as a phase fault, and accordingly shuts the wind turbine down.